The aim of the proposed studies is to learn more about the structure, replication, and synthetic activity of chromosomes in eukaryotic organisms. Four specific areas of concentration are planned: 1. Chromosomal telomeres will be studied using the termini of linear DNA molecules as models. We will examine the unusual extension of the termini that occurs when Tetrahymena rDNA plasmids are injected into eggs of the toad, Xenopus; the addition of CCCCAAAA sequences to the ends of macronuclear DNA molecules in the ciliated protozoan, Euplotes; and the structure of the termini of the two linear mitochondrial DNA molecules of Hydra. In addition, we will attempt to clone telomeres of higher eukaryotes in a linear yeast plasmid. 2. We will continue our studies on RNA transcription during the lampbrush chromosome stage of Amphibian oogenesis with emphasis on the transcription of serially repeated, simple-sequence DNA ("satellite DNA"), and on the recently discovered failure of transcription termination that characterizes the transcription units of these chromosomes. 3. Several putative transposable elements from the toad, Xenopus, will be tested for transposition in a model system. 4. Improvements will be made in the technique of in situ nucleic acid hybridization for RNA in tissue sections.